ABSTRACT

Physical modeling, using ultrasonic sources and receivers over scaled
exploration structures, plays a useful role in wave propagation and
elastic property investigations. This paper explores the anisotropic
response of novel fractured glass blocks created with a laser-etching
technique (Figure 1). We compare transmitted and reflected signals for
P- and S- waves from fractured and unfractured zones in a suite of
ultrasonic experiments. The unaltered glass velocities are 5801 m/s
and 3448 m/s for P and S waves, respectively, with fractured zones
showing a small decrease (about 1%). We estimate high Qp values of
about 1000 for the glass. Signals propagating through the fractured
zone have decreased amplitudes and increased coda
signatures. Reflection surveys (zero-offset and variable polarization
and offset gathers) record significant scatter or diffractions from
the fractured zones. There are hints of frequency dependence on
fracture density. The coda signature may also be an indicator of the
fracture orientation and density. The glass specimens with
laser-etched fractures display a rich anisotropic response.